A data transmission network system typically connects with many terminals for data transmission. A first terminal wishing to send data to a desired second terminal must address the second terminal before transmitting the data.
Facsimile machines (or FAX) were initially designed to transmit and receive image data over the analog Public Switched Telephone Network (PSTN) system in accordance with existing protocols. In the PSTN system, the facsimile machines (i.e. terminals) address each other using numeric addresses, including 0, 1, 2 . . . , 9 and sometimes * and # signs. Typically, the addresses have a fixed length in the PSTN system. Because the PSTN system uses ten numerics (0-9) and possibly two additional signs (0-9, * and #) for addressing, it needs no more than 12 keys to represent the addresses.
By contrast, facsimile machines communicating over switched digital networks use addresses that include ASCII codes because such networks were originally designed for computer systems which can generate and identify ASCII codes.
Digital data transmission over a switched digital network offers advantages contrasted to analog data transmission over the PSTN system. For example, many companies already own private digital networks, perhaps for computer networking. If facsimile machines are coupled to these pre-existing digital networks, literally no extra cost is incurred in using the digital network lines.
Further when the image data are transmitted over a digital network in digital format, encryption of the image data is more easily implemented, thus promoting security. For example, the MIL-STD-188-161 B&C standard is a digital image data transmission protocol mandated by the Department of Defense in the design, development and acquisition of its facsimile equipment.
Digital image data transmission over a switched digital network offers the same advantages mentioned above in the civilian sector, and a G4 digital data transmission protocol is being developed. It seems fair to predict that the future of facsimile data transmissions will be strong in digital network.
Unfortunately, conventional facsimile machines do not have the capability to generate ASCII codes for addressing a switched digital network.
Thus, there is a need to provide facsimile machines that generate ASCII code for addressing a switched digital network.
ASCII codes encompass about 128 different codes, and extended ASCII codes encompass 256 different codes. The most popularly used symbols in ASCII code addressing are alpha-numeric (both upper case and lower case), and some special characters such as ":" and "-". Unlike the PSTN network system, addressing of switched digital network can require different lengths of codes. Therefore, it is impractical to represent each ASCII code with a dedicated key.
Thus, for addressing a switched digital network there is a need to represent at least the more popular address codes without imposing undue hardware overhead on the facsimile machines.
The present invention provides facsimile machines and an implementation method meeting both of these needs.